Grinding machine for welding electrodes

ABSTRACT

A grinding machine for welding electrodes comprises a housing  1 , grinder motor  2 , grinding disk  3 , swing plate  4 , holder guide  6 , electrode holder  7 , electrode turning motor  8  and swing plate moving mechanism  9 . The axis φa of electrode A extends along a line perpendicular to the axis φ of motor drive shaft  2   a  and first grinding part  3   a  of the grinding disk is formed to conform to the finishing contour of electrode A. The grinding disk is turned by the grinder motor and at the same time electrode A is turned by the electrode turning motor. The grinding machine, using one grinding disk, grinds the end portion of an electrode to final form and finishes the tip end of the electrode to a mirror surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to improvements in a grinding machine togrind to a specific shape the end portion of welding electrodes oftungsten, molybdenum, chromium and the like for use in such weldingtechniques as TIG welding and plasma arc welding.

2. Description of the Prior Art

The shape of the end portion of a welding electrode for use in TIGwelding is dependent on factors such as electric current density,current distribution and cooling effects etc. in the welding area andaffects the efficiency of welding work and the welding quality.Therefore, the end portion of the welding electrode is finished to aproper shape, for example, a sharp cone or two-step cut formed of atapered area and a flat area (a so-called “truncated conic shape”)depending, on the material and thickness of the base metal, weldingconditions and other factors. The external surface of the tip of thewelding electrode finished to a specific form is polished to a highdegree of smoothness. Tungsten electrode A for TIG welding as shown inFIG. 12, for example, has a diameter D of 0.5 to 2.0 mm and tapers to ahemispherical tip A₀ with a radius (R) of 0.08 to 0.1 mm. It isdesirable that the external surface of the hemispherical tip A₀ is moresmoothly ground than the tapered section A1 of the electrode. If theexternal surface of the hemispherical tip A₀ is finished to a mirrorsurface or a specular surface, the directivity and stability of the arcwill be substantially improved.

To this end the end portion of the electrode A is usually ground by aspecial electrode grinding machine. Such as the machine shown in FIG. 13and disclosed in unexamined Japanese utility model application No.4-60386 and unexamined Japanese patent application No. 7-276211. Thefollowing two methods are widely adopted. In a first method (hereinafterreferred to as “the first method”), a grinding disk B1 which has arelatively large grain size (#170, for example) is fixed on motor driveshaft M1 is used to grind the end portion of electrode A to a specificform. Then, the grinding disk B1 is replaced with a grinding disk B2which has a finer grain size (#500, for example). By use of the grindingdisk B2, the tip of the electrode is finely ground. In a second method(hereinafter referred to as “the second method”), two grinding machinesare used. One is equipped with grinding disk B1 which has a large grainsize and another with grinding disk B2 which has a fine grain size. Theend portion of the electrode is shaped to a specific form with thegrinding disk B1, and is then finely ground or polished with thegrinding disk B2.

In FIG. 13, the letter C indicates a housing, the letter M a grindermotor, the letter D a grinding disk clamping screw, the letter E a dustcover, and the letter F an electrode guide.

However, the problem with the first method is that two grinding disksB1, B2 have to be changed for each stage of the grinding work andtherefore the grinding process is inefficient and slow.

The second method requires two electrode grinding machines, whichrepresents poor economy and results in increased maintenance costs.

Furthermore, the axial position of electrode A is often dislocated whengrinding disk B1 with a large grain size is replaced with grinding diskB2 with a fine grain size. Accordingly it is difficult to maintain theconcentricity of electrode A. As a result, it takes a substantial periodof time to grind and polish the tip to a mirror surface and furthermore,the form of the tip itself can change in an unintended way.

PROBLEM THAT THE INVENTION IS TO SOLVE

In view of the problems encountered in grinding the end portion of awelding electrode by grinding machines disclosed in the prior art whichare; (1) when working with a grinding machine using a grinding disk witha large grain size and another with a fine grain size, it is troublesometo replace one grinding disk with another each time, and it is difficultto maintain the concentricity of the electrode when the grinding disksare changed, and (2) the use of two grinding machines is expensive andit is difficult to maintain the concentricity of the electrode; it is ageneral object of the present invention to provide a grinding machinefor welding electrodes by which the end portion of even a very shortelectrode can be ground to a specific shape efficiently by a simpleprocedure and only the tip is finished to a mirror surface, i.e. all thegrinding work can be done by this machine alone, and not using twogrinding machines.

SUMMARY OF THE INVENTION

To solve the above-mentioned problems, a particular object of thepresent invention is to provide a grinding machine for weldingelectrodes the grinding machine comprising a box-like housing 1, agrinder motor 2 fixed within the housing 1, a disk-like grinding disk 3fixed on a motor drive shaft 2 a of a grinder motor 2 and provided witha grinding area 3A, a swing plate 4 provided on the housing 1 above thegrinding disk 3 and supported movably in the direction of the axis φ ofa motor drive shaft 2 a, a cylindrical holder guide 6 tumably supportedon the swing plate 4 in a vertical orientation with a downward portionprotruding above the grinding disk 3 in the housing 1, an electrodeholder 7 removably fitted into holder guide 6 and removably clamping anelectrode A with its tip in contact with the grinding area 3A of thegrinding disk 3, an electrode turning motor 8 fixed within the housing 1to turn the holder guide 6 with the electrode holder 7 held therein, anda swing plate moving mechanism 9 for moving the swing plate 4 by aspecific distance 1 along the axis φ of the motor drive shaft 2 a.

A further object of the invention is to provide a grinding machine asdescribed above wherein the grinding area 3A of the grinding disk 3 isformed of a first grinding part 3 a made of coarse grains and a secondgrinding part 3 b made of fine grains.

According to the invention, the grinding disk exhibits several novelfeatures. The grinding area 3A of the grinding disk 3 is formed of—on afront side of the disk—a first grinding part 3 a for grinding an endportion of the electrode A to form a cone and—on an outercircumferential side of the disk—a second grinding part 3 b providedwith a V-shaped grinding groove 3 b′ for grinding a tip A₀ of theelectrode to a mirror surface.

The grinding area 3A of the grinding disk 3 is so constituted that thefirst grinding part 3 a for forming the end portion of the electrode Ain the form of a cone and the second grinding part 3 b for polishing thetip A₀ of the conically formed end portion of the electrode to a mirrorsurface are provided on the front side of the disk. The first grindingpart 3 a is on an inner portion of the disk in the radial direction andon the front side thereof in the thickness direction and the secondgrinding part 3 b is provided on an outer portion of the disk in theradial direction and on said front side thereof but recessed in thethickness direction. The inclination angle α₁ of a longitudinallyinclined surface 3 a ₁ defining the first grinding part 3 a is the sameas that of a longitudinally inclined surface 3 b ₁, defining the secondgrinding part 3 b, wherein the inclination angle α₂ of a transverselyinclined surface 3 a ₂ defining the first grinding part 3 a is the sameas that of a transversely inclined surface 3 b ₂ defining the secondgrinding part 3 b, and the radius R of an arc-like joint between thelongitudinally inclined surface 3 a ₁ and the transversely inclinedsurface 3 a ₂ of the first grinding part 3 a is identical to that of anarc-like joint between a longitudinally inclined surface 3 b ₁ and atransversely inclined surface 3 b ₂ of the second grinding part 3 b. Thegrinding area 3A of the grinding disk 3 is integrally formed of grainswith a medium grain size.

The grinding area 3A of the grinding disk 3 comprises a longitudinallyinclined surface 3 a ₁ to form the end portion of the electrode A intothe shape of a cone, a transversely inclined surface 3 a ₂ to dischargegrinding dust and a curved surface 3 a ₃ to polish the tip A₀ of theelectrode A to a mirror surface.

The grinding area 3A of the grinding disk 3 is formed on both sides of abase of the grinding disk 3 symmetrically.

According to one feature of the invention, one end of the swing plate 4is pivotably fixed on an upper wall of the housing (1) in such a waythat the other end can be moved in the direction of the axis φ of themotor drive shaft 2 a.

According to a further feature of the invention, the electrode holder 7comprises a cylindrical chuck guide 7 a, a collet chuck 7 b to beinserted into an end of the chuck guide and a cylindrical chuck screw 7c inserted into the chuck guide 7 a from an upper side thereof, with thetip portion screwed into the collet chuck 7 b. A spacer 16 with aspecific thickness h may be placed on the chuck guide 7 a so that thetip A₀ of the electrode A is positioned within a grinding groove 3 b′ ofthe second grinding part 3 b.

Another object of the invention is to provide a grinding machine asdescribed above wherein the holder guide 6 with the electrode holder 7held therein is turned by the electrode turning motor 8 via a roundrubber belt 15.

A further object of the invention is to provide a grinding machine forwelding electrodes as described above wherein the swing plate movingmechanism 9 comprises a moving handle 9 a and a worm gear 9 b which isturned by the moving handle and engages with a thread 4 c provided onthe swing plate 4.

Another object of the invention is to provide a grinding machine asdescribed above wherein the distance for which the electrode holder 7 ismoved by the swing plate moving mechanism 9 is indicated by a dial gauge10 having a drive body 10 a which is interlocked with a gauge stopper 4b provided on the swing plate 4.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a grinding machine for welding electrodes inaccordance with the present invention.

FIG. 2 is a side elevation of the grinding machine for weldingelectrodes.

FIG. 3 is a front elevation of the grinding machine for weldingelectrodes.

FIG. 4 is a vertical, sectional side elevation of the essential part ofthe grinding machine for welding electrodes.

FIG. 5 is a vertical, sectional front elevation of the essential part ofthe grinding machine for welding electrodes.

FIG. 6 is a sectional view of a grinding disk.

FIG. 7 is a sectional view of an electrode chuck body.

FIG. 8 is an explanatory view of an electrode grinding extent settinggauge.

FIG. 9 is a sectional view of a grinding disk for welding electrodes inaccordance with a second embodiment.

FIG. 10 is a sectional view of a grinding disk for welding electrodesaccording to a third embodiment.

FIG. 11 is a sectional view of a grinding disk for welding electrodesaccording to a fourth embodiment.

FIG. 12 shows an example of the form of the end portion of a tungstenelectrode for TIG welding.

FIG. 13 shows an example of the prior art grinding machine for weldingelectrodes.

LIST OF NUMERALS

A electrode A

φ axis of motor drive shaft

φ_(a) electrode axis

A₁ tapered section of electrode

A₀ tip end of electrode

1 a case main body

1 b dust cover

1 c clamp

1 d grip

1 e bushing

1 f partition plate

1 g dust case

1 h support component part

1 i hole

1 j storage port

2 grinder motor

2 a drive shaft

2 b grinding disk holder

3 grinding disk

3A grinding area

3 a first grinding part

3 b second grinding part

3 a ₁ longitudinally inclined surface

3 b ₁ longitudinally inclined surface

3 a ₂ transversely inclined surface

3 b ₂ transversely inclined surface

3 b′ grinding groove

3 c base

4 swing plate

4 a support axis

4 b gauge stopper

4 c screw

4 d bushing fixing hole

5 cylindrical bushing

6 holder guide

6 a annulus

6 b pulley

7 electrode holder

7 a chuck guide

7 b collet chuck

7 c check screw

8 electrode turning motor

8 a drive shaft

9 swing plate moving mechanism

9 a moving handle

9 b worm gear

9 c worm box

10 dial gauge

10 a drive body

11 electric control unit

12 grinding extent setting gauge

12 a gauge main body

12 b nut

12 c setting bolt

13 grinding disk clamping screw

14 switch for grinder motors

15 round rubber belt

16 spacer

17 drive pulley

18 switchover limit switch

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the embodiments of the present invention will be described withreference to the drawings.

FIG. 1 is a plan view of a grinding machine for welding electrodes ofthe present invention. FIG. 2 is a side elevation thereof. FIG. 3 is afront elevation thereof. FIG. 4 is a schematic vertical, sectionalelevation thereof. FIG. 5 is a schematic vertical front elevation.

The grinding machine for welding electrodes of the present inventioncomprises a box-shaped housing 1, a grinder motor 2 placed inside thehousing 1, a grinding disk 3 which is turned at a high speed by thegrinder motor 2, a swing plate 4 provided in a front part of an upperwall of the housing 1, a cylindrical bushing 5 fixed vertically in thecentre of the swing plate 4, a cylindrical holder guide 6 rotatablyinserted into the bushing 5, an electrode holder 7 removably insertedinto the holder guide 6 in a vertical position, an electrode turningmotor 8 for turning the electrode holder 7 via holder guide 6, a swingplate moving mechanism 9 to move one side of the swing plate 4supporting the electrode holder 7, a dial gauge 10 to indicate theextent of movement of the electrode holder 7 held by the swing plate 4,and an electric control unit 11 to control the drive of the grindermotor 2 and electrode turning motor 8, etc. In addition, the housing 1is provided with a grinding extent setting gauge 12 to set the extent ofgrinding the electrode, a dresser (not shown) to clean the grindingsurface of the grinding disk 3 and others.

The housing 1 is made in the form of a box and is formed of a housingmain body 1 a made of steel plate or a plastic material with an openingon a front side and a dust cover 1 b made of a transparent plasticmaterial that covers the opening of the front side. In addition, thehousing 1 includes a clamp 1 c to fix the dust cover 1 b, a grip Id andbushings 1 e.

The interior of housing main body 1 a is partitioned by a partitionplate 1 f. A dust case 1 g is removably placed in a lower part of afront compartment.

Furthermore, a support member 1 h for fixing the motors 2, 8 is providedin the rear compartment of the housing main body 1 a.

In the centre of the upper wall of the front compartment of the housingmain body 1 a, there is provided a hole 1 i with a long opening intowhich are inserted the cylindrical bushing 5, the holder guide 6 etc. aswill be described below. Furthermore, a port 1 j to store a grindingextent setting gauge 12 is provided in a one side of the rearcompartment.

The grinder motor 2 is fixed horizontally on a lower side of the supportmember 1 h with a motor drive shaft 2 a extending through the partitionplate 1 f and protruding up into a space above the dust case 1 g of thehousing main body 1 a.

In addition, a grinding disk holder 2 b is fixed on the motor driveshaft 2 a. Furthermore, the grinding disk 3 is removably clamped on thegrinding disk holder 2 b by a grinding disk clamping screw 13.

The grinder motor 2 used in this embodiment is a 100-watt single phasealternating current motor for 100 volts, AC, 50/60 Hz. If a switch 14for grinder motors is turned on, the motor will turn for a specific timepreset by a electric control unit 11 and will be automatically stoppedby a timer switch.

Embodiment 1 of the Grinding Disk

The grinding disk 3 is made in the form of a disk approximately 60 mm indiameter and about 8.2 mm in thickness as shown in FIG. 6. The grindingdisk 3 is fitted over a stepped front end of the grinding disk holder 2b and fixed by said grinding disk clamping screw 13.

The grinding disk 3 is formed of a first grinding part 3 a made ofrelatively coarse diamond abrasive grains and a second grinding part 3 bmade of relatively fine diamond abrasive grains. The first grinding part3 a has a longitudinally inclined surface 3 a ₁ with an inclinationhaving an angle α₁ of approximately 10° with respect to a lineperpendicular to the axis φ of the motor drive shaft 2 a and atransversely inclined surface 3 a ₂ with an inclination angle α₂ ofapproximately 20° with respect to said axis φ. The intersection point Pof the two surfaces is curved with a radius of about 0.08 mm.

The second grinding part 3 b of the grinding disk 3 is formed on anouter circumferential surface of the first grinding part 3 a and has alongitudinally inclined surface 3 b ₁ continuous with the longitudinallyinclined surface 3 a ₁ of the first grinding part 3 a. On the outercircumferential surface of the second grinding part 3 b, there isprovided a V-shaped grinding groove 3 b′ with an opening angle α₃ ofapproximately 10° with a line perpendicular to the axis φ and a depth ofabout 1.2 mm.

In the present embodiment, the first grinding part 3 a is formed ofrelatively coarse diamond abrasive grains about #170 in grain size, andthe second grinding part 3 b is formed of relatively fine diamondabrasive grains about #500 in grain size.

Furthermore, the shortest distance 1 between the line passing theintersection point P, perpendicular to the axis φ and the centre of thegrinding groove 3 b′ is set at about 2.5 mm and the shortest distance hbetween the line passing the intersection point P, parallel to the axisφ and the bottom of the grinding groove 3 b′ is set at about 3.8 mm (foran electrode A 2.0 mm in outside diameter).

Referring to FIGS. 1 to 5, the swing plate 4 is provided on the frontend of the upper side of the housing main body 1 a and one end thereofis pivotably held at one point by a support axis 4 a so that the swingplate 4 can move in the directions of the arrows as shown in FIG. 1.

Another end of the swing plate 4 has a gauge stopper 4 b thereon whichis brought into contact with the tip of a drive body 10 a of the dialgauge 10.

Furthermore, the other end of the swing plate 4 has a screw thread 4 cthat engages with a worm gear 9 b of the swing plate moving mechanism 9,which will be described below.

A bushing fixing hole 4 d is formed in the centre of the swing plate 4.In this bushing fixing hole 4 d, a short cylindrical bushing 5 isinserted to support rotatably said electrode holder 7. And the top ofthe cylindrical bushing 5 is fixed to the swing plate 4.

In the short cylindrical bushing 5, the cylindrical holder guide 6 isrotatably inserted from above. That is, the holder guide 6 is turnablyand movably supported in a vertical position with an annulus 6 a at thetop engaging with an upper end surface of the bushing 5.

The holder guide 6 is to fix removably the electrode holder 7 and iscylindrical in shape as shown in FIG. 4. Said holder guide 6 isrotatably supported in a vertical position on the swing plate 4 via thebushing 5 as mentioned above, and in this holder guide 6, the electrodeholder 7 is removably inserted and fixed.

In addition, a slave pulley 6 b is formed in a lower part of the holderguide 6. A rubber belt 15 connects the slave pulley 6 b and a drivepulley 17 disposed on a drive shaft 8 a of the electrode turning motor8.

The electrode holder 7 is to hold removably and clamp an electrode A insuch a way that a tip of the electrode is in contact with the firstgrinding part 3 a of the grinding disk 3.

The electrode chuck unit 7 comprises, as shown in FIG. 7, a cylindricalchuck guide 7 a to be removably inserted into the holder guide 6, acollet chuck 7 b inserted into an end portion of the chuck guide 7 a anda chuck screw 7 c inserted from an upper side of the chuck guide 7 a andscrewed on and engaged with the collet chuck 7 b. If the electrode A ispassed through the collet chuck 7 b and the chuck screw 7 c is tightenedup, the collet chuck 7 b will squeeze and hold and clamp the electrodeA.

A number of different collet chucks 7 b can be made with differentrespective inside diameters of electrode insertion hole. In the presentembodiment, by electing a collet chuck with an appropriate diameter ofelectrode insertion hole, the grinding machine can accept electrodes Awith diameters between 1.0 mm to 2.6 mm.

In addition, the chuck guide 7 a is so made that a spacer 16 can beremovably fitted on the chuck guide 7 a as shown in FIG. 7. As will bedescribed below, the spacer 16 is used when the tip A₀ of electrode A isground to a mirror surface by the second grinding part 3 b after an endportion of electrode A is formed.

The electrode turning motor 8 is mounted in a rear portion within thehousing main body 1 a and is put on a lower side of the support member 1h.

Said drive pulley 17 is fixed on said drive shaft 8 a of the electrodeturning motor 8. And an endless rubber belt 15 is placed around thedrive pulley 17 and the slave pulley 6 b of the holder guide 6. Thus, ifthe electrode turning motor 8 is turned, the holder guide 6 is drivenvia said endless rubber belt 15, which, in turn, drives the electrodeholder 7 removably clamped in the holder guide 6 and the electrode Afixed therein.

The swing plate moving mechanism 9 comprises a moving handle 9 a, theworm gear 9 b to be turned by said moving handle 9 a, and the thread 4 cat the end of the swing plate 4 engaging said worm gear 9 b and others.If the moving handle 9 a is turned, the worm gear 9 b moves the swingplate 4 in the directions of the arrows using the support axis 4 a as afulcrum.

If the swing plate 4 moves in the directions of the arrows, theelectrode holder 7 fixed on the swing plate 4 moves together with theresult that the tip of electrode A moves in the direction of the axis φof the motor drive shaft 2 a.

The extent to which the swing plate 4 is moved by turning the movinghandle 9 a is shown on the dial gauge 10. That is, as said drive body 10a that is in contact with the gauge stopper 4 b on the swing plate 4moves in the directions of the arrows, the extent of movement of theswing plate 4 is indicated on the dial gauge 10.

It is noted that the dial gauge 10 itself is known and will not beexplained.

The electric control unit 11 is for controlling the operation, includingstartup and stopping of the grinder motor 2 and the electrode turningmotor 8. If the switch 14 for grinder motor is turned on, the two motors2, 8 will turn at a specific speed for a preset time.

To grind and polish the tip of electrode A to a mirror surface using thesecond grinding part 3 b of the grinding disk 3, the two motors 2, 8 areswitched to high speed mode with a greater number of revolutions byactuating a switchover limit switch 18, and the two motors 2, 8 turn ata specific speed for a preset time.

Said grinding extent setting gauge 12 is used to set the protrudingextent of the electrode A held by the electrode holder 7 to decide thegrinding extent of electrode A. The grinding extent setting gauge 12 isremovably stored on one side wall of the housing main body 1 a.

The grinding extent setting gauge 12 comprises, as shown in FIG. 8, acylindrical gauge main body 12 a, a nut 12 b fixed on an end of thegauge main body 12 a and a setting bolt 12 c screwed into the nut 12 b.With the electrode holder 7 inserted into the gauge main body 12 a, thetip of electrode A is brought into contact with the setting bolt 12 cwhich controls the extent to which the electrode A protrudes out of theelectrode holder 7.

In this regard, the grinding extent setting gauge 12 is used in thefollowing way. First, the electrode A is held and clamped in theelectrode holder 7 with its tip portion protruding by a specific length.Then, the electrode holder 7 is inserted into the holder guide 6 and theelectrode A is test-ground on the first grinding part 3 a of thegrinding disk 3. Then the electrode is checked to see if the end portionis ground to a perfect cone. If electrode A is ground perfectly, theelectrode holder 7 with electrode A held and clamped thereon is takenout and placed in the gauge main body 12 a, and the setting bolt 12 c ismoved to adjust the gap between the tip of the electrode A and the endof the setting bolt 12 c to a specific distance, 0.5 mm, for example.Once the grinding extent setting gauge is set this way, the grindingextent of the electrode A can be adjusted and fixed simply by thisgauge.

Next, the grinding of an electrode A using the grinding machine forelectrodes of the present invention will be described.

The first step is to select a grinding disk 3 that is suitable forelectrode A with regard to its diameter and the grinding shape of theend portion. This grinding disk 3 is placed on the motor drive shaft 2a. Then, the electrode A is inserted into the collet chuck 7 b of theelectrode holder 7. With its tip portion protruded by a specific length(45 mm to 50 mm) from the end of the collet chuck 7 b, the electrode Ais slidably held by lightly tightening the chuck screw 7 c.

The electrode holder 7 with said electrode A held therein is insertedinto the gauge main body 12 a of the grinding extent setting gauge 12and, with the tip of the electrode A in contact with the setting bolt 12c, the electrode A is pushed back though the collet chuck 7 b. And whenthe electrode holder 7 is fully fitted into the gauge main body 12 a,the chuck screw 7 c is tightened up to clamp the electrode A. Thus, theprotruding extent and the grinding extent of electrode A are now set. Itis assumed that the electrode A has been test-ground as mentioned aboveand that the position of the setting bolt 12 c of the grinding extentsetting gauge 12 has been adjusted properly.

Then, the electrode holder 7 is inserted into the holder guide 6 toplace the tip of the electrode A on the first grinding part 3 a of thegrinding disk 3, and then the switch 14 is turned on.

While the electrode A turns, its tip is kept in contact with the firstgrinding part 3 a of the grinding disk 3 and gradually ground. As theelectrode A is ground, the electrode holder 7 slides down through theholder guide 6 under its own weight, and the end portion of electrode Ais automatically ground in the form of a cone. When the electrode holder7 slides down by a certain distance, a knob of the chuck guide 7 a comesto rest on an upper end of the holder guide 6, preventing the electrodeholder 7 from sliding down any further.

When the electrode A is ground for a specific time, the timerautomatically switches off the motors 2, 8 with the conical formgrinding completed. When the electrode A has been ground to a conicalshape the electrode holder 7 is pulled out of the holder guide 6 and thespacer 16 is put on the electrode holder 7.

Then, while watching the dial gauge 10, the moving handle 9 a of theswing plate moving mechanism 9 is turned to move the position of theaxis of the holder guide 6 inwardly (i.e. in the direction of the centreof the housing 1) by a specific distance 1. Thus, the tip of electrode Aheld by the electrode holder 7 comes just above the second grinding part3 b of the grinding disk 3 when the electrode holder 7 is placed in theholder guide 6.

After the swing plate 4 is moved to its new position, the spacer 16 isput on the chuck guide 7 a of the electrode holder 7. And the electrodeholder 7 with the spacer 16 put thereon is placed in the holder guide 6.

The thickness of the spacer 16 is set to dimension h mentioned above.Thus, the tip of cone shaped electrode A held in the electrode holder 7contacts the V-shaped grinding groove 3 b′ of the second grinding part 3b.

If the switch 14 for the grinder motor is now turned on again, thegrinding disk 3 and the holder guide 6 turn at a specific high speed fora specific time, and the electrode holder 7 moves down some 1.2 mm underits own weight. As a result, a spherical portion of the tip of electrodeA is ground to a mirror surface by the fine-grained second grinding part3 b.

It is noted that when the swing plate 4 is moved, the switchover limitswitch 18 is actuated to automatically switch the two motors 2, 8 to ahigh speed. And the hemispherical tip of the electrode A is finished toa mirror surface with great efficiency.

Embodiment 2 of the Grinding Disk

FIG. 9 shows a second embodiment of the grinding disk 3. As with thegrinding disk 3 of the first embodiment the grinding disk 3 of thesecond embodiment is made in the form of a disk about 60 mm in diameterand about 8.2 mm in thickness. The grinding disk 3 is placed on thestepped part of the front end portion of the grinding disk holder 2 band clamped to the grinding disk holder 2 b by tightening up theclamping screw 13.

As is shown in FIG. 9, the grinding disk 3 has a first grinding part 3 amade of relative coarse grains of about #170 and a second grinding part3 b made of relatively fine grains of about #500. The first grindingpart 3 a and the second grinding part 3 b are formed as step formationson the front side of the disk.

That is, the first grinding part 3 a is provided on the front side ofthe disk in an inner portion in the radial direction. The first grindingpart 3 a has a longitudinally inclined surface 3 a ₁ having aninclination with an angle α₁ of approximately 10° with respect to a lineperpendicular to the axis φ of the motor drive shaft 2 a, and atransversely inclined surface 3 a ₂ having an inclination angle α₂ ofapproximately 20° with respect to the axis φ. A joint P between the twoinclined surfaces is curved in the form of an arc with a radius R ofapproximately 0.08 mm.

The second grinding part 3 b is provided outside the first grinding part3 a in the radial direction and on the front side but recessed in thethickness direction, and has a longitudinally inclined surface 3 b ₁having an inclination angle α₁ of approximately 10° with the lineperpendicular to the axis φ of the motor drive shaft 2 a and atransversely inclined surface 3 b ₂ having an inclination with an angleα₁ of approximately 20° with respect to the axis φ. An arc-shaped jointQ between the two inclined surfaces is curved with a radius R ofapproximately 0.08 mm.

The distance 1 in the thickness direction of the disk (that is, thedrive shaft direction of the grinder motor) is about 2.5 mm between thearc-like joint P of the first grinding part 3 a and the arc-like joint Qof the second grinding part 3 b, and the distance h in the radialdirection of the disk is set at some 3.8 mm (for electrode A with anoutside diameter of 2.0 mm).

In the second embodiment, the first grinding part 3 a and the secondgrinding part 3 b are identical in terms of their angles α₁, α₂ andradius R. Needless to say, they may be made different from each other.

Also, this second embodiment is identical to the first embodiment interms of distance 1 and distance h. Again, needless to say, a differentdistance 1 and a different distance h may be adopted in the secondembodiment.

The procedure of grinding the electrode A using the grinding disk 3 inthe second embodiment is exactly the same as that in the firstembodiment and will not be explained.

In the grinding disk 3 of the second embodiment, the second grindingpart 3 b is open on the front side, and does not have a V-shaped grooveas in the first embodiment. Therefore, the second grinding part 3 b ishardly clogged. That substantially saves labour needed for maintenanceand care of the grinding disk 3.

Embodiment 3 of the Grinding Disk

FIG. 10 shows a third embodiment of the grinding disk 3. As shown inFIG. 10, the grinding disk 3 is some 60 mm in diameter and about 8.2 mmin thickness and is integrally formed of diamond abrasive grains(abrasive material) of a medium grain size (#350, for example) betweencoarse grains (#170, for example) and fine grains (#500, for example).The grinding disk 3 is put on the stepped part of the grinding diskholder 2 b and clamped by the grinding disk clamping screw 13.

The grinding disk 3 is provided with a grinding area 3A to grind the endportion of the electrode A. Said grinding area 3A is formed in a shapecorresponding to the finished shape of the end portion of the electrodeA as shown in FIG. 12.

That is, the grinding area 3A is defined by a longitudinally inclinedsurface 3 a ₁ having an inclination angle α₁ of approximately 10° withrespect to the line perpendicular to the axis φ of the motor drive shaft2 a that grinds the end portion of the electrode A into the shape of acone, a transversely inclined surface 3 a ₂ having an inclination angleα₂ of approximately 20° with respect to the axis φ of the motor driveshaft 2 a that serves to discharge grinding dust, etc., and a curvedsurface 3 a ₃ or an arc-like joint between the two inclined surfaceswith a radius R of approximately 0.08 mm that grinds the tip A₀ of atapered section A1 of the electrode A into a hemispherical mirrorsurface (for electrode A with an outside diameter D=2.0 mm).

To grind the electrode A, the electrode holder 7 is inserted into theholder guide 6 and, with the tip of electrode A in contact with thegrinding area 3A of the first grinding part 3 a, the switch for thegrinder motor 14 is turned on, as in the case of the first embodiment.

Then, the grinding disk 3 is turned about the axis φ by the grindermotor 2, and at the same time the electrode A is turned around the axisφ_(a) by the electrode turning motor 8.

In this way, the electrode A turns and the end portion thereof is groundon the grinding area 3A of the grinding disk 3 with which the electrodeA is in contact. As the electrode A is ground, the electrode holder 7moves down in the holder guide 6 under its own weight. And the endportion of the electrode A is automatically shaped to a cone by thelongitudinally inclined surface 3 a ₁ of the grinding disk 3. At thesame time, the tip of the electrode A is ground and finished to ahemispherical mirror surface by the curved surface 3 a ₃ of the grindingdisk 3.

The reason why the electrode A is ground and finished that way is asfollows. It is so arranged that the axis φ_(a) of the electrode Aextends along a line perpendicular to the axis φ of the motor driveshaft 2 a, and the grinding area 3A of the grinding disk 3 has a formcorresponding to the finished shape of the electrode A. Furthermore, thegrinding disk 3 is turned by the grinder motor 2, and at the same timethe electrode A is turned by the electrode turning motor 8.

When the electrode holder 7 has moved down by a specific distance, theknob of the chuck guide 7 a comes into contact with the top end of theholder guide 6 and hence electrode holder 7 is prevented from movingdown any further.

When the grinding continues for a certain time, the timer switchautomatically stops the motors 2, 8, and the grinding is finished. Theelectrode holder 7 is pulled out of the holder guide 6, and electrode Ais taken out of the electrode holder 7. Then electrode A is obtainedwith the end section in the form of a conic taper A₁ and with the tipend A₀ finished to a hemispherical, mirror surface as shown in FIG. 12.

To grind an electrode A with a different outside diameter or to adjustthe grinding extent, the moving handle 9 a of the swing plate movingmechanism 9 is turned to move the position of the axis of the holderguide 6 along the axis φ of the motor drive shaft 2 a by a specificdistance while watching the dial gauge 10 so as to adjust the contactbetween the electrode A and the grinding disk 3.

In the preceding example, the grinding area 3A of the grinding disk 3 isprovided with a longitudinally inclined surface 3 a ₁, and the curvedsurface 3 a ₃ is matched to the finished shape of the electrode A asshown in FIG. 12. The present invention is not limited to that. Toobtain an electrode A with an end portion having two tapered sectionswith different angles, that is, a two-step conical form, the grindingarea 3A may be provided with a two-stepped inclination contour, that is,two longitudinally inclined surfaces.

Embodiment 4 of the Grinding Disk

FIG. 11 shows a fourth embodiment of the grinding disk 3. This grindingdisk 3 has two grinding areas 3A of the third embodiment symmetricallyformed on both sides of a base 3 c so that each of the two grindingareas 3A can be used in turn.

The procedure of grinding by this grinding disk 3 is the same as that bythe grinding disk 3 of the third embodiment and will not be repeated.

Effects of the Invention

a. In the present invention, it is so arranged that the axis of theelectrode extends along a line perpendicular to the axis of the motordrive shaft and that the grinding part of the grinding disk is so formedto conform to the finished shape of the electrode. Furthermore, when thegrinding disk is turned by the grinder motor, the electrode is turned bythe electrode-turning motor at the same time. Therefore, using onegrinding disk and one grinding machine for electrodes, it is possible toshape the end portion of an electrode to a final form and finish the tipto a mirror surface.

b. In the present invention, there is provided a two-part grinding disk3 comprising a first grinding part 3 a formed of coarse grains with alarge grain size and a second grinding part 3 b formed of fine grainswith a fine grain size. And it is so arranged that the swing plate 4turnably supporting the electrode holder 7 is moved by the swing platemoving mechanism 9, and an end portion of the electrode A is ground bythe first grinding part 3 a and the second grinding part 3 b.

By this arrangement, the end portion of the electrode is conicallyshaped by the first grinding part 3 a with relatively large abrasivegrains and only the tip A₀ of the electrode is polished to a mirrorsurface by the second grinding part 3 b with relatively fine abrasivegrains with great efficiency.

It is also noted that, with electrode A held in the electrode holder 7,the end portion of the electrode is conically shaped and the tip A₀ isfinished to a mirror surface using the same grinding machine forelectrodes, and therefore, even when grinding is switched from conicalform grinding to mirror polishing, there is no dislocation to theposition of the axis of the electrode, and the tip A₀ can be finished toa mirror surface efficiently and precisely.

c. In the present invention, it is so arranged that the electrode holder7 is moved exactly by a specific distance 1 by the swing plate movingmechanism 9 while watching the dial gauge 10. In addition, the turningdriving force is transferred to electrode A by the endless rubber belt15, which absorbs fluctuations in the distance 1 by shrinking orexpanding. As a result, the electrode holder 7 is turned smoothly.

d. By merely inserting the spacer 16 in the electrode holder 7, it ispossible to adjust the height of the tip end A₀ of the electrode A to aspecific elevational position and to grind precisely the tip A₀ alone toa mirror surface.

e. In the present invention, the grinding disk is also formed integrallyof grains with the same grain size (medium grain size), with thegrinding area shaped to conform to the finished contour of theelectrode. That makes the manufacture easy and reduces the cost ofmanufacture.

f. Also in the present invention, the axis of the electrode extendsalong a line perpendicular to the axis of the motor drive shaft. Thatsubstantially simplifies the construction and reduces the cost ofmanufacture as compared with such grinding machines in which thegrinding disk itself is slanted against the electrode or the slant angleis adjusted.

g. In the present invention, it is possible to move the electrode holderby the swing plate moving mechanism while watching the dial gauge, whichpermits very precise positioning of the electrode in relation to thegrinding disk.

What is claimed is:
 1. A grinding machine for welding electrodes, saidgrinding machine comprising: a box housing; a grinder motor fixed in thehousing; a grinding disk provided with a grinding area and fixed on adrive shaft of said grinder motor; a swing plate provided above thegrinding disk and on the housing and supported movably in the directionof the axis φ of the drive shaft; a cylindrical holder guide rotatablysupported by the swing plate in a vertical position with a lower portionprotruded above the grinding disk in the housing; an electrode holderwhich is removably fitted into the holder guide, and which removablyclamps an electrode with an end portion thereof in contact with thegrinding area of the grinding disk; an electrode turning motor which isfixed in the housing and which turns the holder guide with the electrodeholder fitted therein; and a swing plate moving mechanism which movesthe swing plate along the axis φ of the motor drive shaft by a specificdistance L.
 2. The grinding machine for welding electrodes as defined inclaim 1, wherein the grinding area of the grinding disk is formed of afirst grinding part made of coarse grains and a second grinding partmade of fine grains.
 3. The grinding machine for welding electrodes asdefined in claim 1, wherein the grinding area of the grinding disk ismade so that a first grinding part for shaping an end portion of theelectrode in the form of a cone is provided on a front side of the diskwhile the second grinding part is provided with a V-shaped groove forpolishing a tip of the conically formed end portion of the electrode toa mirror surface, wherein the V-shaped groove is provided on an outerperipheral portion of the disk.
 4. The grinding machine for weldingelectrodes as defined in claim 1, wherein the grinding area of thegrinding disk is constructed so such that a first grinding part forforming the end portion of the electrode in the form of a cone, and asecond grinding part for polishing the tip of the conically formed endportion of the electrode to a mirror surface, are both provided on afront side of the disk respectively.
 5. The grinding machine for weldingelectrodes as defined in claim 4, wherein said first grinding part isprovided on an inner portion of the disk in the radial direction and onthe front side thereof in the thickness direction, and the secondgrinding part is provided on an outer portion of the disk in the radialdirection and on said front side thereof but recessed in the thicknessdirection.
 6. The grinding machine for welding electrodes as defined inclaim 5, wherein an inclination α₁ angle of a longitudinally inclinedsurface defining the first grinding part is the same as that of alongitudinally inclined surface defining the second grinding part;wherein an inclination angle α₂ of a transversely inclined surfacedefining the second grinding part is the same as that of a transverselyinclined surface defining the second grinding part; and wherein a radiusof an arc joint between the longitudinally inclined surface and thetransversely inclined surface of the first grinding part is identical tothat of an arc joint between a longitudinally inclined surface and atransversely inclined surface of the second grinding part.
 7. Thegrinding machine for welding electrodes as defined in claim 1, whereinthe grinding area of the grinding disk is integrally formed of grainswith a medium grain size.
 8. The grinding machine for welding electrodesas defined in claim 7, wherein the grinding area of the grinding disk isprovided with a longitudinally inclined surface for shaping the endportion of the electrode in the form of a cone, a transversely inclinedsurface for discharging grinding dust, and a curved surface forpolishing a tip A₀ of the electrode to a mirror surface.
 9. The grindingmachine for welding electrodes as defined in claim 1, wherein thegrinding area of the grinding disk is formed symmetrically on each sideof the base of the grinding disk.
 10. The grinding machine for weldingelectrodes as defined in claim 1, wherein one end of the swing plate ispivotably fixed on an upper side of the housing in such a way thatanother end of the swing plate can be moved in the direction of the axisφ of the motor drive shaft.
 11. The grinding machine for weldingelectrodes as defined in claim 1, wherein the electrode holder comprisesa cylindrical chuck guide, a collet chuck to be inserted into an endside of a chuck guide and a cylindrical chuck screw inserted into thechuck guide from an upper side thereof and with a tip portion screwedinto the collet chuck.
 12. The grinding machine for welding electrodesas defined in claim 11, wherein a spacer with a specific thickness h isput on the chuck guide of the electrode holder so that a tip of theelectrode is positioned within a grinding groove of the second grindingpart.
 13. The grinding machine for welding electrodes as defined inclaim 1, wherein the holder guide with the electrode holder held thereinis turned by the electrode turning motor via an endless rubber belt. 14.The grinding machine for welding electrodes as defined in claim 1,wherein the swing plate moving mechanism comprises a moving handle and aworm gear which is turned by the moving handle and engages with a threadprovided on the swing plate.
 15. The grinding machine for weldingelectrodes as defined in claim 14, wherein the distance L by which theelectrode holder is moved by the swing plate moving mechanism isindicated by a dial gauge having a drive body which is interlocked witha gauge stopper provided on the swing plate.